The invention relates to reducing the size of catheter tip measurement devices that are inserted into body organs to make internal measurements. More specifically, the invention relates to the mechanism for supporting and insulating an electrical measurement sensor, particularly a semiconductor strain gauge pressure transducer, that is located at the distal tip of a catheter tip measurement device.
Catheter tip measurement devices are catheters that have measurement sensors located at or near their distal tips. These devices are used in a variety of applications to measure internal properties of internal tissues and fluids such as blood volume, velocity and pressure. Catheter tip measurement devices may be introduced directly into arteries, veins or other body organs either by themselves or through other catheters that have been previously positioned within a patient. Catheter tip measurement devices generally have electrical or fiber optic connectors at the proximal end of the catheter that communicate data from the measurement sensors to external processing devices. Catheter tip pressure transducers are catheter tip measurement devices that have at least one pressure transducer located at or near the distal tip of the catheter.
The size of the catheter tip is important, and for many applications, this size is the primary limiting factor that determines whether a measurement catheter may be used in a particular application. For example, size is important and is a limiting factor in measuring pressure within small vessels, such as coronary arteries. Size is also important where a catheter tip measurement device is being introduced through the lumen of another catheter. One such application is where a small sized catheter tip pressure transducer is introduced through the lumen of an electrode or conductance catheter. A conductance catheter has electrodes disposed at the distal end of the catheter to measure electrical currents. These measurements can be translated into volume and impedance measurements of heart segments on a beat-by-beat basis. A catheter tip pressure transducer introduced through the lumen of a conductance catheter allows for simultaneous measurement of pressure at the tip of the conductance catheter. In this way, the conductance catheter can be used for volume measurements, and the catheter tip pressure transducer can be used for pressure measurements. The resulting pressure/volume loops are of significant diagnostic value in many types of heart disease.
Studies involving small animals are further important applications where a small catheter size is desirable and often required. Although small sized fluid-filled catheters may be used for internal pressure measurements, they are typically reliable only when catheters with relatively large lumens are used and when slow heart beat rates are involved. In small animals, however, the heart beat rates are typically very fast, and the organ size is very small. The internal fluid-filled lumen of the fluid-filled catheter will generally be so small in such applications that the pressure signals received will tend to be extremely damped and unreliable. Although prior catheter tip pressure transducers provide the desired high-fidelity, prior devices have been too large for small animal applications. As more and more research is being done on mice instead of larger animals such as rats, dogs or monkeys, the need for small catheters capable of providing high fidelity internal pressure measurements will continue to increase.
Present small-size catheter devices capable of making internal pressure measurements take the form of fluid-filled devices, electrical strain gauge type transducer devices, and fiber optic devices. Fluid-filled devices may have very small construction, but such devices provide poor measurement fidelity. Similarly, fiber optic devices have a very small sensor size, but such devices have relatively unstable and unacceptable performance. In contrast, strain gauge type transducer devices, which utilize semiconductor pressure transducers, provide high-fidelity measurements but suffer from requiring a significantly larger feature size.
What is needed, therefore, is a catheter tip pressure transducer device that provides high-fidelity measurements with the stability of electrical strain gauge devices and with a very small feature size. What is also, and more generally, needed is the capability of reducing the tip size of catheter tip measurement devices.